Aspergillus flavus grown in peptone as the carbon source exhibits spore density- and peptone concentration-dependent aflatoxin biosynthesis

Abstract

BackgroundAflatoxins (AFs) are highly carcinogenic compounds produced by Aspergillus species in seeds with high lipid and protein contents. It has been known for over 30 years that peptone is not conducive for AF productions, although reasons for this remain unknown.ResultsIn this study, we showed that when Aspergillus flavus was grown in peptone-containing media, higher initial spore densities inhibited AF biosynthesis, but promoted mycelial growth; while in glucose-containing media, more AFs were produced when initial spore densities were increased. This phenomenon was also observed in other AF-producing strains including A. parasiticus and A. nomius. Higher peptone concentrations led to inhibited AF production, even in culture with a low spore density. High peptone concentrations did however promote mycelial growth. Spent medium experiments showed that the inhibited AF production in peptone media was regulated in a cell-autonomous manner. mRNA expression analyses showed that both regulatory and AF biosynthesis genes were repressed in mycelia cultured with high initial spore densities. Metabolomic studies revealed that, in addition to inhibited AF biosynthesis, mycelia grown in peptone media with a high initial spore density showed suppressed fatty acid biosynthesis, reduced tricarboxylic acid (TCA) cycle intermediates, and increased pentose phosphate pathway products. Additions of TCA cycle intermediates had no effect on AF biosynthesis, suggesting the inhibited AF biosynthesis was not caused by depleted TCA cycle intermediates.ConclusionsWe here demonstrate that Aspergillus species grown in media with peptone as the sole carbon source are able to sense their own population densities and peptone concentrations to switch between rapid growth and AF production. This switching ability may offer Aspergillus species a competition advantage in natural ecosystems, producing AFs only when self-population is low and food is scarce.

Effects of different substrates and oils on aflatoxin B1 production by Aspergillus parasiticus

“…Spore inoculum was prepared as described by Yan et al [23]. Sixty microlitre of A. parasiticus spore suspensions stored at −80 °C in 20 % glycerol was sub-cultured on potato dextrose agar plates at 37 °C for 4 days.…”

Toxigenic potentiality of Aspergillus flavus and Aspergillus parasiticus strains isolated from black pepper assessed by an LC-MS/MS based multi-mycotoxin method

“…According to Georgianna and Payne, (2009) the 442 regulation of STERIG and especially aflatoxin production by Aspergillus generally require simple 443 sugars, low pH, reduced nitrogen source and mild oxidative stress. Recent studies have even shown 444 that when A. flavus was grown in peptone-containing media, higher initial spore densities inhibited 445 aflatoxin biosynthesis, but promoted mycelial growth (Yan et al, 2012). However, it is still hard to say 446 that this could be the reason in our substrate for its observed low AFG production, since they still 447 produced high level of B aflatoxins.…”

Comparative study: bench-scale surfactin production from bacillus subtilis using analytical grade and concentrated glycerol from the biodiesel industry

“…Peptides can be absorbed into the cell and metabolized into amino acids. Then, by deamination or oxidative deamination, these amino acids are converted into intermediates of tricarboxylic acid cycle such as serine → pyruvate, aspartate → oxaloacetate, glutamate → 2-oxoglutarate [24][25]. However, the catabolic pathways of many amino acids remain unknown or only partially characterized.…”

“…However, the catabolic pathways of many amino acids remain unknown or only partially characterized. In this context, arginine and histidine are known to provide energy [24][25]. Yan et al [25] evaluated the aflatoxin production from Aspergillus flavus using a culture medium comprised by salts and peptone as sole carbon source.…”

“…In this context, arginine and histidine are known to provide energy [24][25]. Yan et al [25] evaluated the aflatoxin production from Aspergillus flavus using a culture medium comprised by salts and peptone as sole carbon source. They indicated that Aspergillus flavus preferred peptone as a sole carbon source for growth rather than traditional fermentable sugars.…”